The present invention relates to a coder of moving picture signals used for recording, communications, transmissions, broadcasting, etc., and in particular to a motion vector detecting method and a motion vector detecting system for motion compensating predictive coders which can code differences between motion vector data (representative of an area from which motion vectors move on a coded picture) and areas indicated by the motion vector data.
In video signals of multi-gradation such as television (TV) or photograph, since the quantity of video data is huge, when the digital video signals are processed (e.g., transmitted, recorded, etc.) in an unencoded format, a transmission path of wide frequency band and a recording medium of large capacity are inevitably required. Therefore in a video signal processing apparatus handling TV (visual) telephone, TV (visual) conference, cable television service (CATV), picture filing apparatus, etc., a coding technique for compressing the huge video signals down to a small quantity of data is required. As one of the moving picture coding methods, steps are performed as follows: a highest correlation area relative to a partial area of an input picture is detected on a coded reference picture; motion vector data indicative of from which area the partial area of the input picture moved on the coded reference picture is determined; and a difference between the partial area of the input picture and the detected partial area indicated by the motion vector data is coded.
On the other hand, as a scanning method for pictures, there exist methods of non-interlaced scanning (scanned one by one in sequence) and interlaced scanning (scanned every other line or alternately). An imperfect picture obtained by interlaced scanning (ore line is omitted between scanning lines) is referred to as a field, and a perfect picture obtained by one non-interlaced scanning or two interlace scannings is referred to as a frame.
In the case where no motion exists between two fields of the same frame, as with the case of the interlaced scanning picture, it is often effective to adopt the motion compensating predictive method using motion vector data detected on the basis of frame construction.
In contrast with this, in the case of the interlaced scanning picture, since some motion exists between the two fields in the same frame, it is often effective to adopt the motion compensating predictive method using motion vector data detected on the basis of the field construction.
Therefore, in the conventional method, in order to cope with both the cases where motion exists between two fields of the same frame and where no motion exists, the motion vector has been so far detected separately for both the partial area formed by the input picture frame and the partial area formed by a field separated according to the field phase. Further, the predictive distortion (obtained when one motion vector detected for the partial area formed by the frame is used) is compared with the addition of the predictive distortions (obtained when two motion vectors detected for two partial areas of two fields for constituting the same frame are used), and the motion vector is compensated for so that these distortions can be minimized in the conventional predictive coding method.
In the conventional motion vector detecting method, however, motion vector detection at a partial area of the frame of the input picture and the motion vector detection at a partial area of the field are executed separately. In other words, in order to obtain the motion vector for a partial area of the input picture, the calculation for detecting one frame motion vector and the calculation for detecting two field motion vectors are executed independently at a wide search window. There is thus a problem in that a huge quantity of calculations is required.